During operation of reciprocating internal combustion engine, the valve can be opened and closed regularly through the valve driving mechanism, such that the engine can effectively absorb fresh air or combustible mixture, and can discharge the exhaust gas from the cylinder. After a valve driving mechanism is designed, movement of the valve is fixed. Valve lift and duration of valve opening cannot be adjusted according to actual operations of the engine.
The engine of automobile is running in all conditions. In design, it is necessary to take into account both power in high load and economy in low load. However, the fixed movement of the valve endows the engine a best state only in a particular working condition. It is unable to reconcile the demands of power and economy in most cases for the engine.
In order to overcome such defect of the engine, variable valve lift systems are increasingly used in engines. However, existing variable valve lift systems are complex in structure and difficult to manufacture, and the duration of valve opening cannot be adjusted.